[Qemu-devel] [PATCH] vl: prevent SDL replacing 'main' on win32 platforms

["Daniel P. Berrange" <berrange@redhat.com>]

The SDL provided 'main' replacement on Win32 redirects
stdout and stderr to text files, which in turn prevents
QEMU from using the console for the monitor (eg -monitor
stdio breaks), and also hides error messages and -help
output from the user.

Block SDL's replacement by simply undefining the 'main'
macro, so the QEMU binaries' 'main' symbol takes priority
over that found in SDL.dll

The SDL replacement is left in place for other platforms,
since it might be doing something more important on
them. It would be worth investigating if it can be removed
for OS-X though as a future cleanup.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
---
 vl.c | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/vl.c b/vl.c
index 0adbbd6..bb9ed8b 100644
--- a/vl.c
+++ b/vl.c
@@ -39,7 +39,23 @@
 #endif
 
 #ifdef CONFIG_SDL
-#if defined(__APPLE__) || defined(main)
+#if defined(_WIN32)
+/*
+ * On Win32 SDL tries to rename 'main' to 'SDL_main' so it can
+ * insert itself into the startup sequence, by passing the
+ * compiler flag -Dmain=SDL_main. It does this so it can mess
+ * with startup, amongst other dubious things, replacing stdout
+ * and stderr with streams pointing to a file instead of the
+ * console. This in turn breaks ability of QEMU to use stdio for
+ * things like the monitor (eg no more -monitor stdio), and error
+ * reporting, even if SDL is not the current UI frontend.
+ *
+ * The SDL startup hacks appear to not be critical to the correct
+ * functioning of SDL on Win32, so block SDL's attempt to hijack
+ * 'main' and thus avoid broken console I/O
+ */
+#undef main
+#elif defined(__APPLE__) || defined(main)
 #include <SDL.h>
 int qemu_main(int argc, char **argv, char **envp);
 int main(int argc, char **argv)
-- 
2.4.3